Electrochemical capacitor having double electrical layer

ABSTRACT

The invention relates to electrical engineering and can be used for developing energy-storing devices. The inventive electrochemical double-layer capacitor makes it possible to develop an operable device having a long service life in addition to high specific energy and power. Said electrochemical double layer capacitor comprises a molten electrolyte (4) provided with a gelling agent.

FIELD OF THE INVENTION

The invention relates to the field of electrotechnique and can be usedfor creating devices accumulating electrical energy and utilized:

in systems of emergency power supply when operating in a constant orcompensation recharge mode;

to ensure constant power supply when employing energy sources actingperiodically, i.g., in wind or helio-power industry;

in devices accumulating energy of recuperative braking at transport;

as traction batteries for electric transport.

BACKGROUND OF THE INVENTION

The action principle of the known capacitor having a double electriclayer, or electro-chemical capacitor, is based on utilizing energyaccumulated in the double electric layer which appears at the border offirst and second class conductors (electrode—electrolyte).

As a rule, electrodes in such capacitors are made from carbon materialswith high specific surface. Power capacity of the capacitor is limitedby a decomposition voltage and capacitance of the double electric layer,which are inherent for an electrolyte being employed. In the case ofaqueous electrolyte, the decomposition voltage is 1.23 V.

Known is a capacitor having a double electric layer, including twoelectrodes and aqueous electrolyte (RU 2054723 C1, H 01 G 9/00, 1996).

Use of organic solvents as electrolyte permits to raise an operatingvoltage of the capacitor up to 3-4 V.

Known is a capacitor having a double electric layer, including twoelectrodes and organic electrolyte (U.S. Pat. No. 3,700,975 A, H 01 G9/00, 1972).

However, realization of great powers in the capacitor having a doubleelectric layer and organic electrolyte is impeded due to lowconductivity of the latter.

The analogue closest to the proposed solution by its technical essenceis a capacitor having a double electric layer and including polarizableelectrodes, separator and molten electrolyte (U.S. Pat. No. 5,621,607 A,H 01 G 9/04, 1993).

In the known capacitor, molten chlorides and bromides are used aselectrolyte.

For example, in an electrolyte from eutectic mixture of potassium andlithium chlorides at 400-500° C., a capacitance of an electrode fromactivated carbon material having a surface of 900-1,200 m²/g isapproximately 500 F/g, and having a surface of 1,500-2,000 m²/g is 600F/g. Conductivity of this electrolyte is 1.7 Ohm/cm at 400° C. Thedecomposition voltage for molten aluminum and magnesium chloridesexceeds 2.5 V, for alkali metal chlorides −3.5 V, and for fluorides −5V.

Use of molten salts is attended with solving a series of problems boundwith their high corrosion aggresiveness at high temperatures in relationto structure materials of the body, electric conductors etc.

These problems are so serious that they could not create a capacitorhaving molten electrolyte and possessing a resource and lifetimeacceptable for practice.

SUMMARY OF THE INVENTION

The problem being solved by the proposed capacitor having a doubleelectric layer is to create an efficient device with a great resourceand lifetime in combination with high specific energy and power.

The technical result in the solution being proposed is achieved bycreating a capacitor having a double electric layer, includingelectrodes, at least one of which is polarizable, separator and moltenelectrolyte, wherein in accordance with the invention a stiffener isintroduced into a composition of molten electrolyte.

The invention is characterized in that as the stiffener is used aninert, fine disperse material.

Materials can be powders having particles of any form (includingfibers).

The invention is characterized in that as the stiffener is used a finedispersed material on the basis of oxides, or mixed oxides, nitrides ofaluminum, or magnesium, or calcium, or strontium, or boron, or silicon,or zirconium, or yttrium, or beryllium, or mixtures thereof.

Use of molten salts, i.g., halogenides of elements of the first andsecond groups of the main subgroup of the periodic system as electrolyteallows to increase significantly specific capacitance of the capacitor,since a capacitance of the double electric layer of theelectrode-electrolyte (melt) border exceeds significantly the same inaqueous electrolyte, and especially in organic one.

The invention is also characterized in that the second electrode is madenon-polarizable and comprises, as the active material, substancescapable to oxidize and reduce reversibly in electro-chemical manner inan environment of this molten electrolyte.

This permits to increase specific energy of the capacitor.

It is possible to use, as the active material, metals of the first, orsecond, or third groups of the periodic system, or mixtures thereof, ortheir alloys with carbon, or silicon, or boron, or other metals.

Metal and alloy can be formed during a charge of the capacitor.

They are used as the negative electrode.

The non-polarizable electrode comprises, as the active material,sulfides or oxides of metals from group of iron, or vanadium, or chrome,or copper, or mixtures thereof, and they are used as an active mass ofthe positive electrode.

Introduction of the stiffener into the composition of electrolyte allowsto create a capacitor having a double electric layer (element), in whichthe molten electrolyte is fastened at the cost of capillary force in theactive electrode material and stiffener, and does not contact with thebody details. In such an element, the stiffened electrolyte cansimultaneously serve as a separator.

This allows, first, to avoid corrosion of construction materials, and,second, to create a bodyless element-capacitor having a double electriclayer.

The molten electrolyte may comprise various amount of stiffener, i.e.,may have various degree of stiffness.

At a lower content of stiffener the electrolyte conductivity andcapacitor capacitance increase, at higher content of stiffener themechanical stability of the system is raised.

The essence of the proposed capacitor having a double electric layer isexplained by the following description and examples as well as FIG. 1which shows schematically the capacitor construction.

PREFERRED EMBODIMENTS

The capacitor having a double electric layer includes electrodes 1 and2, at least on of which electrodes is polarizable, a separator 3, anactive electrode material 4, a molten electrode 5, a stiffener 6introduced into the electrolyte content, electric conductors 7.

Trials of the proposed construction were carried out with employment ofvarious materials used as a stiffener, active electrode material etc.

It is expedient to use, as a material of the polarizable electrode,conductive material with high specific surface, stable in theenvironment of the molten electrolyte (activated carbon, carbides,nitrides, oxides, metals).

The obtained results are shown in the examples described below.

EXAMPLE 1

Electrodes of the capacitor are made from activated carbon powder havingthe surface of 900-1,200 m²/g (20-30 mass %) with an addition ofelectrolyte, and produced in the form of discs 22 mm in diameter and 1.2mm wide. Electrolyte comprises an eutectic mixture of lithium andpotassium chlorides (59 mol. % LiCl) with the melting temperature of352° C. Powder of magnesium aluminate (40 mass %) is introduced into theelectrolyte as a stiffener. A separator (i.e., a stiffened electrolyteof the same composition) is made in the form of a pressed plate 1 mmwide. Graphite discs 24 mm in diameter and 0.3 mm wide serve as electriccontacts.

EXAMPLE 2

In contrast with the Example 1, the electrodes are made from activatedcarbon powder having specific surface 1.500-2.000 m²/g.

EXAMPLE 3

In contrast with the Example 1, one electrode is made in the form of aplate from powder of ferric disulfide (FeS₂) with addition ofelectrolyte 0.5 mm wide.

EXAMPLE 4

In contrast with the Example 1, one electrode is made in the form of aplate from powder of lithium-aluminum alloy (2-4 mass % of lithium) 0.5mm wide.

Industrial Applicability

Characteristics of capacitors at 400° C. in accordance with the setforth examples are shown in the Table.

On the basis of the proposed capacitor having a double electric layer itis possible to create a battery of bipolar construction, including asmany elements combined in a single body as is wished to obtain anecessary voltage. Absence of bodies for each element will facilitatesignificantly a battery construction and reduce its weight.

TABLE Characteristics of capacitors described in the Examples ParametersExample 1 Example 2 Example 3 Example 4 Maximum voltage, V 3.0 3.0 2.03.0 Capacitance, F 31 40 70 59 Discharge current, A 0.5 0.5 0.5 0.5Internal resistance, Ohm 0.2 0.2 0.2 0.2 Electrode surface, cm² 3.7 3.73.7 3.7 Mass of element, g 1.7 1.7 1.5 1.3 Specific energy, 23 29 26 56W · h/kg Maximum specific 6.6 6.6 3.3 8.6 power, kW/kg

What is claimed is:
 1. A capacitor having a double electric layer,including electrodes, at least one of the electrodes being polarizable,a separator and a molten electrolyte, wherein a stiffener is introducedinto the composition of the molten electrolyte.
 2. The capacitor havinga double electric layer according to claim 1, wherein as the stiffeneris used an inert, fine disperse material introduced into theelectrolyte.
 3. The capacitor having a double electric layer accordingto any of claims 1-2, wherein as the stiffener is used a fine dispersedmaterial on the basis of oxides, or mixed oxides, nitrides of aluminum,or magnesium, or calcium, or strontium, or boron, or silicon, orzirconium, or yttrium, or beryllium, or mixtures thereof.
 4. Thecapacitor having a double electric layer according to claim 1, whereinthe molten electrolyte comprises halogenides of elements of the first,or second, or third groups of the main subgroup of the periodic system,or mixtures thereof.
 5. The capacitor having a double electric layeraccording to claim 1, wherein one of the electrodes is non-polarizableand comprises, as an active material, substances capable to oxidize andreduce reversibly in electro-chemical manner in an environment of themolten electrolyte.
 6. The capacitor having a double electric layeraccording to claim 5, wherein the non-polarizable electrode comprises,as the active material, metals of the first, or second, or third groupsof the periodic system, or mixtures thereof, or their alloys withcarbon, or silicon, or boron, or other metals.
 7. The capacitor having adouble electric layer according to claim 5, wherein the non-polarizableelectrode comprises, as the active material, sulfides or oxides ofmetals from group of iron, or group of vanadium, or group of chrome, orgroup of copper, or mixtures thereof.